Method of imparting flame resistant properties to nylon and the treated product

ABSTRACT

Nylons are rendered resistant to a self-sustaining flame by treating the surface thereof with certain methylol compounds.

United States Patent 2,139,190 12/1938 lselin etal Inventor Roland J. Bryan, Jr.

Pensacola, Fla.

Appl. No. 766,285

Filed Oct. 9, 1968 Patented Nov. 16, 1971 Assignee Monsanto Company St. Louis, Mo.

METHOD OF IMPARTING FLAME RESISTANT PROPERTIES T0 NYLON AND THE TREATED PRODUCT 6 Claims, No Drawings References Cited UNITED STATES PATENTS 8/1945 Bauer et a1 260/561 UX 7/1959 Ohnacker et a1. 260/559 1/1960 Morettiet 117/136X 9/1960 Bumell 117/138.8 X 7/1964 Metivier et a1. 260/559 X 6/1967 Lafon 260/559 X 5/ 1 969 Schoot 260/5 5 8 8/1969 Raynolds et a1. 117/1383 X FOREIGN PATENTS 5/1951 Great Britain 260/558 Primary Examiner-William D. Martin Assistant Examiner-Harry J. Gwinnell Attorneys-John W. Whisler and Stanley M. Tarter ABSTRACT: Nylons are rendered resistant to a self-sustaining flame by treating the surface thereof with certain methylol compounds.

METHOD OF IMPARTING FLAME RESISTANT PROPERTIES TO NYLON AND THE TREATED PRODUCT BACKGROUND OF THE DISCLOSURE It is recognized in the art that most polymers can be rendered resistant to a self-sustaining flame by preparing the polymers in the presence of certain halogen-containing organic compounds, known as flame retardants. However, halogenated flame retardants cannot be incorporated into nylon since they decompose when subjected to the high temperatures encountered in nylon polymerization. In an attempt to circumvent this problem halogenated flame retardants have been applied as a finish to nylon fibers and fabrics. However, the retardants, when applied as a finish, are not bonded to the nylon surface and consequently are easily removed therefrom, for example, by washing of the fabric. This technique is therefore unsatisfactory since it provides only temporary protection to the fabric.

An object of the invention therefore is to provide a novel class of halogen-containing organic flame retardants.

Another object of the invention is to provide shaped nylon articles which have a permanent ability to resist a self-sustaining flame.

i ll -CN and A-OCILCN CHgOH wherein A is a halogencontaining organic radical having from one to 20 carbon atoms. The treated articles are then dried and heat-set at a temperature below the decomposition temperature of the methylol compound, for example, at l50 C. for minutes. Higher or lower temperatures may be used by merely adjusting the residence time.

When nylon shaped articles are treated with the abovedescribed methylol compounds in accordance with the invention, the methylol compounds are chemically bonded to the backbone of the nylon molecules. The term nylon as used herein has its usual significance, that is, it refers to synthetic linear polycarbonamides containing recurring carbonamide linkages as an integral part of the polymer chain, i.e.,

in which R is a hydrocarbon radical having at least two carbon atoms. Representative nylons include nylon 6 (poly-e-caprolactam), nylon 66 (polyhexamethylene adipamide), nylon 6/10 (polyhexamethylene sebacamide), nylon ll, (poly-maminoundecanoid acid), and the like. Although the precise mechanism involved in the bonding of the methylol compounds to the nylon molecules is not known with absolute certainty, it is believed that the mechanism which takes place when nylon is treated with an acid solution of the methylol compounds is as follows:

Methylol compounds of the formula:

if AOCH CN CI-LOH react according to the same mechanism as do the methylol compounds of the formula:

3 /II ACN CH OII Since the treatment described herein results in a chemical bonding of the methylol compounds to the nylon molecules, the ability of the treated articles to resist a self-sustaining flame is of a permanent nature. Moreover, the treatment does not plasticize or change the melting point of the nylon. The amount of methylol compound required to impart flame retardant properties to nylon varies depending on the degree of flame retardancy desired and also on the ratio of halogen atoms to carbon atoms of the particular methylol compound being used. Generally, nylon having from 0.05 to 5.00 percent by weight of the methylol compound bonded to its surface exhibit satisfactory flame retardant properties, although lesser or greater amounts in some instances may be desirable.

PREFERRED EMBODIMENTS OF THE INVENTION Suitable methylol compounds for use in the invention are those of the above formulas in which A is a halogen-containing aliphatic or aromatic organic radical having from one to 20 carbon atoms, such as halogen-containing radicals selected from the group consisting of aryl, alkaryl, alkyl, aralkyl and alkenyl, which radicals may also contain substituent groups in addition to halogen atoms, provided such groups do not alter the character of the treated nylon, e.g., they may contain carbonyl or nitro groups. Moreover, the compounds may contain one or a plurality of halogen atoms. Best flame retardant properties are obtained when the methylol compounds contain at least one halogen atom for every l0 carbon atoms.

The preferred compounds are those in which A is a C l to C halogen-containing organic radical selected from C, C alkyls, phenyl and naphthyl radicals, wherein the halogen atom or atoms are chlorine or bromine. Examples of compounds of this type are Nmethylol-2, Z-dichloroacetamidc; N-methylol- 2-chloracetamide; N-methylol-2-(3,3-dichloroethoxy)acetamide; N-methylol-2-(p-bromophenoxy )acetamide; N- methylol-2(2, 4, o-tribromophenoxy)acetamide; N-methylolp-chlorobenzamide; and N-methylol-2-(a-chloronaphthoxy)acetamide.

The compounds of the invention are conveniently prepared by refluxing a haloacetamide and formaldehyde in an organic inert diluent, such as chloroform, to which sufficient sodium hydroxide has been added to make the medium basic.

The invention is further illustrated but not limited by the following examples in which the percentages unless designated otherwise are by weight.

EXAMPLE I Preparation of N-methylol-Z-chloroacetamide: The following ingredients were charged to a flask fitted with a stirrer and water condenser and heated at reflux for 18 hours:

Z-chloroacetamide 32.7 g. (0.349 mole) formaldehyde 29.2 g. of a 36% aqueous solution (0.349 mole) chloroform 700 cc.

NaOH enough to basify (approx.

Upon cooling the reaction product, a white solid material precipitated and was separated by filtration. The material was recrystallized from chloroform giving a melting point range of 825C. to 835C.

EXAMPLE 2 Preparation of N-methylol-2-(p-bromophcnoxy)acetamide:

The following ingredients were refluxed for l7 hours according to the procedure of example 1.

2-(p-bromophenoxy)aeetamide, grams 13. 8 Formaldehyde, grams 5. chloroform, cubic centimeters 350 NaOH, grams 0. 3

36% aqueous solution.

Upon cooling a white solid material precipitated which was separated by filtration and recrystallized from methanol. The resulting product had a melting range of l47 C. to 148 C.

EXAMPLE 3 Preparation of N-methylol-p-chlorobenzamide:

The following ingredients were refluxed for 22 hours according to the procedure of example I.

p-chlorobenzamide 50 5. formaldehyde 3l.l g. chloroform 750 cc. NIOH 0.3 g.

Upon cooling a white material precipitated which was separated by filtration and recrystallized twice from water. The resulting product had a melting range of 175 C. to 178 C.

EXAMPLE 4 Fabric treatment.

Four identical samples of nylon 66 tricot fabric were scoured with a standard scouring solution of 5 percent Triton X-lOO, which is a nonionic surfactant, and Spercent tetrasodium pyrophosphate for 30 minutes at290 C. The samples were then rinsed in deionized water six times at290 C. for 30 minutes each and dried in an oven at 150 C. for 15 minutes, followed by further drying in a dessicator for 5 minutes. The samples were then accurately weighed and each immersed in one of the following solutions for at least 1 minute, removed (allowing the excess solution to drip away), dried in an oven at 150 C. for 15 minutes, followed by scouring, drying and weighing in the same matter as before.

Solution I I01: N-methylol-2-chloroacetamide and 1% H,S0, in deionized water 2 N-methylol-Z-(p-bromophenoxy)acetamide and llv H,SO in deionized water 3 2.2% N-methylol-p-chlorobenz2mide in water adjusted to a pH of to 2, with [1,50,

4 deionized water adjusted to a pH of l to 2 with ",SO, (control) The amount of pickup of the methylol compound is given in the following table Flame Testing Analysis of Samples: I

Each of the fabric samples treated in example 4 was analyzed for flammability with the apparatus designated for this purpose in A.S.T.M. Designation D1230 and according to the procedure described therein for its operation. The results of the analysis are given in table 2.

TABLE 2 Fabric Treated With Solution Burning Characteristics I Will not propagate a flame in any direction; burns less than I second.

2 Supports a flame for about 3 seconds in a small circular area (less than one inch in diameter).

3 Burned for IS seconds in a circular manner (about one inch and did not project up the incline.

Supported a flame rather well for 45 seconds in all directions including projection all the way up the incline.

4 (control) The data in table 2 illustrate that nylon 66 fabric treated with the methylol compounds of the invention have an ability to resist a self-sustaining flame even when only small amounts of the compounds are employed (0.79 percent on weight of fabric), whereas in the absence of treatment nylon fabric supports a flame rather well.

Although the invention has been illustrated with reference to the treatment of nylon 66 with particular methylol compounds, similar results are also obtained when articles fabricated from other nylons are treated with any of the methylol compounds described herein.

lclaim: v

1. Nylon modified to containing as an integral part of its polymer chain at least 0.05 percent by weight of a unit selected from the group consisting of v a: A-CN and AOCIlz-C in which A is selected from the group consisting of chlorinecontaining organic radicals and bromine-containing organic radicals, wherein said radicals have from one to 20 carbon atoms, characterized in that said unit is attached directly to a nitrogen atom of said chain.

2. The modified nylon of claim I wherein the nylon is polyhexamethylcne adipamide.

3. The modified nylon of claim 2 wherein A is a chlorinecontaining hydrocarbon radical having from one to 10 carbon atoms.

4. The modified nylon of claim 3 wherein A is ClCH,-.

5. The modified nylon of claim 3 wherein A is in which X is chlorine or bromine and n is an integer from one to five.

6. A method of imparting flame resistant properties to nylon shaped articles which comprises:

a. treating the surface of said article with a liquid having a in which A is selected from the group consisting of chlorinepH of less than 7 and containing a compound selected containing organic radicals and bromine-containing radifrom the group consisting of cals, wherein said radicals have from one to 20 carbon H O H atoms; ll H g b. drying the treated article; and A C and AOCHC c. heatsetting the treated article.

CHzOH CH OH =0: 1: a a: t 

2. The modified nylon of claim 1 wherein the nylon is polyhexamethylene aDipamide.
 3. The modified nylon of claim 2 wherein A is a chlorine-containing hydrocarbon radical having from one to 10 carbon atoms.
 4. The modified nylon of claim 3 wherein A is ClCH2-.
 5. The modified nylon of claim 3 wherein A is
 6. A method of imparting flame resistant properties to nylon shaped articles which comprises: a. treating the surface of said article with a liquid having a pH of less than 7 and containing a compound selected from the group consisting of 